When acceptability of a tire shape is to be determined, a rubber material portion which is a tire main body portion constituting an outer peripheral portion is attached to a ring-shaped metal component (rim) constituting an inner peripheral portion of a tire, and after the inside is filled with air, an appearance shape of a tire side portion (sidewall), for example, is grasped and acceptability is determined.
As such methods for grasping tire appearance shapes, a method using a three-dimensional shape measuring method called a light section method (See Patent Literature 1) and a method using an optical displacement sensor (See Patent Literature 2) are known.
Here, the light section method is a method of irradiating a tire surface (sidewall, for example) along a radial direction of a tire with light (line light) linearly focused by a cylindrical lens or the like, photographing the shape of the line light on the tire surface by a camera or the like, and measuring a surface shape of the tire at a light irradiated portion (linear portion) according to the principle of triangulation from the obtained photographed image. By using this method, for example, performing the measurement at certain rotation angle intervals while rotating the tire makes it possible to grasp the sidewall shape of the entire periphery of the tire.
On the other hand, the optical displacement sensor focuses emitted light from a laser or the like into a spot shape (point shape) to irradiate the tire surface therewith, receives its reflected light by a linear image sensor such as CCD, and measures a height of the tire surface at a light irradiated portion (point-shaped portion) from a change in the position of the reflected light. Since the optical displacement sensor measures only the height of the point-shaped portion irradiated with light, as described above, when the surface shape of the sidewall is to be measured, for example, a plurality of the optical displacement sensors is juxtaposed for use in the radial direction of the tire to perform measurement at certain rotation angle intervals while rotating the tire similarly to the light section method so that the sidewall shape of the entire periphery of the tire is grasped.
However, with the above-described prior-art methods, after the measurement data of the tire appearance shape (hereinafter referred to as “tire contour measurement data”) is obtained, since contour deformation caused by deflection is not corrected, the contour of a deflected tire cannot be inspected correctly.
Hence, if the tire appearance shape is measured by the above-described prior-art methods, the tire main body should be incorporated in the rim and air should be filled, and an internal pressure should be raised to a state where there is no deflection caused in the tire, and thus, there is a problem that preparation time for the measurement becomes long and productivity lowers.